Seed Starting Mix with Coco Coir Giving Horrible Results

I had mentioned before that I didn't have enough ProMix BX to start all of the plants in so I tried a coco coir seed starting mix for a few of the plants.  At first I thought 3 plants were just a little slow getting going, but now it is obvious that the plants started in the coco coir are the ones that are stunted.   Wish I could remember what brand I used, because I know some people start seeds in coco coir without problems, but these plants have obvious problems.   I gave them a mild fertilizer today, because I have to believe the issue is nutrient based.  Most seed starting mixes have very little in them, so I don't know what the issue would be with this coco coir, but I won't use it ever again.

If any Utah grower knows of a place to buy ProMix please let me know.